1. Field of the Invention
The invention relates in general to escalators or moving stairways, and more specifically to new and improved arrangements for guiding passenger conveyors of this type.
2. Description of the Prior Art
An escalator includes an endless belt having a plurality of steps attached thereto. The endless belt and steps are driven through a load-bearing run which includes combplates at each end of the run, a balustrade on each side of the run for guiding a handrail, and skirt panels disposed immediately adjacent to each side of the run. It is desirable to provide a very small running clearance between the steps and the skirt panels. It is essential that the grooves in the step treads mesh properly with the teeth at the combplates. Thus, an escalator must be accurately guided laterally during its travel about the endless loop.
Many different guiding arrangements have been taught in the prior art. For example, escalators may be laterally guided by upstanding guide portions disposed on the tracks which support the main step wheels or rollers, one each side of the endless belt. The sides of the step wheels contact the guide portions on the tracks when a dimensional lateral limit is reached, in either lateral direction. The scuffing action between the sides of the wheels and the guiding portions of the tracks produces noise and wear, necessitating frequent lubrication in order to reduce the noise and wear to acceptable values.
Another prior art arrangement guides the steps from the back side of the skirts via a plurality of auxiliary wheels which bear against auxiliary guide angle members fastened to the skirts.
In both of these arrangements, the escalator is guided from both sides of the endless belt. Laterally guiding both sides of the endless belt, however, makes the positions of both the right- and lef-hand guides critical, requiring jigs and fixtures for accurately positioning the guide angle members on both sides of the escalator during manufacture. Further, the field installation and alignment of both guides is critical.
Thus, certain prior art arrangements disclose guiding an escalator from only one side of the endless belt, removing the criticality in the placement of the track on the other side of the escalator. For example, U.S. Pat. No. 4,064,986, which is assigned to the same assignee as the present application, discloses an escalator in which the guiding function is performed from one side of the escalator by guide wheels and a guide track, with the contacting portions of the guide wheels and the guide track being non-flat. An upthrust limit function is provided by guard wheels mounted coaxially with the guide wheels on the same side of the endless belt, and a guard track disposed on the opposite side of the rotational axis of the guide and guard wheels as the guide track. The guard wheels, in cooperation with the contoured guide wheels also function to limit lateral movement of the endless belt and connected steps.
While the structure taught by the U.S. Pat. No. 4,064,986 has many advantages over prior art escalator guiding arragenments, it would be desirable to be able to provide the advantages of this structure without the addition of guard wheels. The guard wheels taught in this patent protect the non-flat surfaces of the guide wheels from damage at transition sections, by supporting the weight of the conveyor across these sections on auxiliary tracks. The guard wheels also limit lateral movement of the endless belt and steps when subjected to severe side thrust forces, such as might be caused by the entrapment or wedging of an article between a step and a skirt panel. However, even with this limit on lateral movement, lateral movement may occur which allows a moving step to contact the adjacent stationary skirt panel, especially when the running clearance is at the low end of the dimensional range, which is typically 0.090 to 0.180 inch.
Thus, it would be desirable to provide a new and improved guiding arrangement for an escalator which guides from one side of the endless belt, which prevents damage to the guide wheels at transition points, and which limits side travel of the endless belt to a dimension less than the minimum normal running clearance dimension, while eliminating the additional guard wheels proposed by the hereinbefore mentioned U.S. Pat. No. 4,064,986.